1. ADDING AND
SUBTRACTING
DECIMALS
SECTION 1.07

2. RULES
• LINE UP DECIMALS
– If you can not drop a straight line down
through your decimals, they are not lined up
correctly
– Add zeros as placeholders if needed
• BRING YOUR DECIMAL STRAIGHT DOWN
• ADD OR SUBTRACT AS USUAL

3. Add & Subtract like Columns
7.1 + 5.8 + 2.5 = _______
ones
RULE: Only add
and subtract
LIKE columns.
1
7.1
5.8
+ 2.5
15 . 4
tenths

4. Make The Columns Even
34.5 + 21 + 8.5
RULE: Add zeros to
even the columns
34.5
21.0
+ 8.5
34.5
21.0
+ 8.5

5. Make The Columns Even
44.589 + 7.23 + 5
3 decimal 2 decimal
columns columns
0 decimal
columns
1
1
44.589
7.230
+ 5 .000
56.819

6. Subtract Similar Columns
34 – 1.2 = _____
ones
tenths
34. 0
- 1. 2
32 . 8
33

8. FRONT-END ESTIMATION
• Adding the numbers in front of the
decimals
• Rounding the decimal numbers to the
nearest whole number
• Add the two sums

9. EXAMPLE
•
For your birthday you receive a $25 gift certificate. You
want to buy 2 used video games, whose prices are:
$8.79, $7.29, $ 7.89 Can you buy all 3 games using the
gift certificate?
1. Add the front-end digits
$8 + 7 + 7 = $22
2. Estimate the sum of the remaining digits (what is
behind the decimal)
.79 and .29 are about $1
.89 is about $1
$1 + $1 = $2
3. Add the results.
$22 + $2 = $24
The estimated sum is less then $25, so you can buy all 3
with your gift card.